Colorants for use in tinted contact lenses and methods for their production

ABSTRACT

The invention provides a colorant for use in tinting contact lenses in which the binding polymer used is capable of forming an interpenetrating polymer network with the lens material. When the colorants of the invention are applied to uncured lens material that is subsequently cured, the binding polymer forms an interpenetrating polymer network with the lens material embedding the colorant within the lens material resulting in a stable, tinted lens.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of U.S. Ser. No.09/792,671 (VTN-530) filed Feb. 21, 2001.

FIELD OF THE INVENTION

[0002] The invention relates to colorants useful in the production oftinted contact lenses. In particular, the invention provides a one stepprocess for tinting contact lenses and colorants for use in the process.

BACKGROUND OF THE INVENTION

[0003] The use of tinted contact lenses to alter the natural color ofthe iris is well known. Generally, the tinted portion of the lens islocated in the center of the lens, the portion of the lens that willoverlay either or both the pupil and iris of the lens wearer. It is alsowell known in the tinting of contact lenses that the entire lens may belightly tinted as a visibility or locator tint.

[0004] Colorants used to produce tinted lenses generally are composed ofa binding polymer and pigments. The known colorants require the use ofcrosslinking agents to form covalent bonds between the lens materialsand the binding polymer in order to form stable, tinted lenses. By“stable, tinted lenses” is meant that the tints do not bleed or leachout from the lens or from one portion of the lens to another.Additionally, in some of the known methods for forming tinted lenses, itis required that the lens body be formed prior to the introduction ofthe colorant onto the lens. Other processes and colorants requiremultiple steps for use alone or in conjunction with specialized rings toprotect the outer portions of the lens from the colorant.

[0005] Thus, the known colorants and processes for producing tintedlenses introduce one or both of additional time and additional materialsinto the normal lens manufacturing process. Therefore, a need exists fora colorant, and method for producing contact lenses using the colorant,that eliminate some or all of these disadvantages.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[0006] The invention provides colorants for use in the manufacture oftinted contact lenses, and a method for the tinting of contact lensesusing the colorants of the invention. When the colorants of theinvention are applied to uncured lens material that is subsequentlycured, the binding polymer forms an interpenetrating polymer networkwith the lens material. Thus the colorant becomes embedded within thelens material resulting in a stable, tinted lens. This is advantageousin that the colorants do not require the use of covalent bonds to aid inthe entrapment of the colorant's pigment within the lens. Further, thecolorants of the invention transfer from a mold surface to the lensmaterial in a way that results in a finished lens with a high resolutionimage of the pattern printed using the colorant.

[0007] In one embodiment, the invention provides a colorant for use intinting contact lenses, the colorant comprising, consisting essentiallyof, and consisting of: one or more pigments, one or more solvents, and abinding polymer, wherein the binding polymer is capable of forming aninterpenetrating polymer network with a lens material. In anotherembodiment, the invention provides a method for manufacturing a tintedcontact lens comprising, consisting essentially of, and consisting ofthe steps of: a.) applying to a molding surface of a mold atinting-effective amount of a colorant, the colorant comprising,consisting essentially of, and consisting of: one or more pigments, oneor more solvents and a binding polymer; b.) dispensing a lens-formingamount of a lens material into the mold; c.) swelling the colorant inthe lens material and diffusion of the lens material into the colorant;and d.) curing the lens material in the mold under conditions suitableto form the tinted contact lens, wherein the binding polymer and thelens material form an interpenetrating polymer network. In yet anotherembodiment, the invention provides a mold for use in manufacturing atinted contact lens comprising, consisting essentially of, andconsisting of a first and second mold half, wherein at least one moldingsurface of the first and second mold halves comprises, consistsessentially of, and consists of: one or more pigments, one or moresolvents, and a binding polymer, wherein the binding polymer is capableof forming an interpenetrating polymer network with a lens material.

[0008] For purposes of the invention, “interpenetrating polymer network”or “IPN” is defined as the combination of two or more independentpolymers in which one polymer is synthesized and/or cross-linked in thepresence of the other. Thus, some degree of interpenetration occurswithin the network structures. Typically, the independent polymers usedto form the IPN are in network form. One type of IPN, specifically asemi-IPN, is composed of one or more polymers that are cross-linked andone or more polymers that are not substantially cross-linked asdisclosed by “Interpenetrating Polymer Networks: An Overview” bySperling, L. H. in Interpenetrating Polymer Networks, Edited byKlempner, Sperling, and Utracki, pp 3-6(1994). For purposes of theinvention, the type of interpenetrating polymer network used is asemi-IPN. In one embodiment, the semi-IPN is formed using a lensmaterial, which is crosslinked and a binding polymer which is notsubstantially crosslinked. For the purposes of this invention notsubstantially crosslinked means that the non-crosslinked material is notsubjected to conventional crosslinking conditions prior to contact withthe lens material. Semi-IPNs may be formed in one step, or in a seriesof steps, which are known as sequential semi-IPNs. One of ordinarilyskilled in the art will recognize that, the presence of cross-linkingagents, either through addition or as impurities, can create a reactionenvironment that favors the formation of a sequential interpenetratingpolymer network.

[0009] For purposes of the invention, by “molding surface” is meant amold surface used to form a surface of a lens.

[0010] It is a discovery of the invention that by using a bindingpolymer that is capable of forming an interpenetrating polymer networkwith a lens material, the need for formation of covalent bonds betweenthe colorant and lens material to form a stable, tinted lens iseliminated. Stability of the tinted lens is provided by entrapment ofthe pigments within entanglements of the binding polymer and the lensbase polymer. The binding polymers of the invention are made from ahomopolymer or copolymer, or combinations thereof, having similarsolubility parameters to each other and the binding polymer has similarsolubility parameters to the lens material. These binding polymers maycontain functional groups that render the polymers and copolymers of thebinding polymer capable of interactions with each other. The functionalgroups must be such that the groups of one polymer or copolymer interactwith that of another in a manner that increases the density of theinteractions helping to inhibit the mobility of and/or entrap thepigment particles. The interactions between the functional groups may bepolar, dispersive, or of a charge transfer complex nature. Thefunctional groups may be located on the polymer or copolymer backbonesor be pendant from the backbones.

[0011] For example, a monomer, or mixture of monomers, that form apolymer with a positive charge may be used in conjunction with a monomeror monomers that form a polymer with a negative charge to form thebinding polymer. As a more specific example, methacrylic acid (“MAA”)and 2-hydroxyethylmethacrylate (“HEMA”) may be used to provide aMAA/HEMA copolymer that is then mixed with a HEMA/3-(N, N-dimethyl)propyl acrylamide copolymer to form the binding polymer.

[0012] As another example, the binding polymer may be composed ofhydrophobically-modified monomers including, without limitation, amidesand esters of the formula:

CH₃(CH₂)_(x)—L—COCHR═CH₂

[0013] wherein L may be -NH or oxygen, x may be a whole number from 2 to24, R may be a C₁ to C₆ alkyl or hydrogen and preferably is methyl orhydrogen. Examples of such amides and esters include, withoutlimitation, lauryl methacrylamide, and hexyl methacrylate. As yetanother example, polymers of aliphatic chain extended carbamates andureas may be used to form the binding polymer.

[0014] Preferred binding polymers of the invention are a random blockcopolymer of HEMA, MAA and lauryl methacrylate (“LMA”), a random blockcopolymer of HEMA and MAA or HEMA and LMA, or a homopolymer of HEMA. Theweight percentages, based on the total weight of the binding polymer, ofeach component in these embodiments is about 93 to about 100 weightpercent HEMA, about 0 to about 2 weight percent MAA, and about 0 toabout 5 weight percent LMA.

[0015] The molecular weight of the binding polymer must be such that itis somewhat soluble in the lens material and swells in it. The lensmaterial diffuses into the binding polymer and is polymerized and/orcross-linked. However, at the same time, the molecular weight of thebinding polymer cannot be so high as to impact the quality of theprinted image. Preferably, the molecular weight of the binding polymeris about 7,000 to about 100,000, more preferably about 7,000 to about40,000, most preferably about 17,000 to about 35,000 M_(peak) whichcorresponds to the molecular weight of the highest peak in the SECanalyses (=(M_(n)×M_(w))^(½))

[0016] For purposes of the invention, the molecular weight is determinedusing a gel permeation chromatograph with a 90° light scattering andrefractive index detectors. Two columns of PW4000 and PW2500, amethanol-water eluent of 75/25 wt/wt adjusted to 50 mM sodium chlorideand a mixture of polyethylene glycol and polyethylene oxide moleculeswith well defined molecular weights ranging from 325,000 to 194 areused.

[0017] One ordinarily skilled in the art will recognize that, by usingchain transfer agents in the production of the binding polymer, by usinglarge amounts of initiator, by using living polymerization, by selectionof appropriate monomer and initiator concentrations, by selection ofamounts and types of solvent, or combinations thereof, the desiredbinding polymer molecular weight may be obtained. Preferably, a chaintransfer agent is used in conjunction with an initiator, or morepreferably with an initiator and one or more solvents to achieve thedesired molecular weight. Alternatively, small amounts of very highmolecular weight binding polymer may be used in conjunction with largeamounts of solvent to maintain a desired viscosity for the bindingpolymer. Preferably, the viscosity of the binding polymer will be about4,000 to about 15,000 centipoise at 23° C.

[0018] Chain transfer agents useful in forming the binding polymers usedin the invention have chain transfer constants values of greater thanabout 0.01, preferably greater than about 7, and more preferably greaterthan about 25,000. Suitable such chain transfer agents are known andinclude, without limitation, aliphatic thiols of the formula R—SHwherein R is a C₁ to C₁₂ aliphatic, a benzyl, a cyclicalipahtic orCH₃(CH₂)_(x)—SH wherein x is 1 to 24, benzene, n-butyl chloride, t-butylchloride, n-butyl bromide, 2-mercapto ethanol, 1-dodecyl mercaptan,2-chlorobutane, acetone, acetic acid, chloroform, butyl amine,triethylamine, di-n-butyl sulfide and disulfide, carbon tetrachlorideand bromide, and the like, and combinations thereof. Generally, about 0to about 7 weight percent based on the total weight of polymerformulation will be used. Preferably dodecanethiol, decanethiol,octanethiol, or combinations thereof is used as the chain transferagent.

[0019] Any desirable initiators may be used including, withoutlimitation, ultra-violet, visible light, thermal initiators and the likeand combinations thereof. Preferably, a thermal initiator is used, morepreferably 2,2-azobis isobutyronitrile and 2,2-azobis2-methylbutyronitrile. The amount of initiator used will be about 0.1 toabout 5 weight percent based on the total weight of the formulation.Preferably, 2,2-azobis 2-methylbutyronitrile is used with dodecanethiol.

[0020] The binding polymers of the invention may be made by anyconvenient polymerization process including, without limitation, radicalchain polymerization, step polymerization, emulsion polymerization,ionic chain polymerization, ring opening, group transfer polymerization,atom transfer polymerization, and the like. Preferably, athermal-initiated, free-radical polymerization is used. Conditions forcarrying out the polymerization are within the knowledge of oneordinarily skilled in the art.

[0021] Solvents useful in the production of the binding polymer aremedium boiling solvents having boiling points between about 120 and 230C. Selection of the solvent to be used will be based on the type ofbinding polymer to be produced and its molecular weight. Suitablesolvents include, without limitation, diacetone alcohol, cyclohexanone,isopropyl lactate, 3-methoxy 1-butanol, 1-ethoxy-2-propanol, and thelike.

[0022] The binding polymer of the invention is tailored, in terms ofexpansion factor in water, to the lens material with which it will beused. Matching or substantially matching the expansion factor of thebinding polymer with that of the cured lens material in packing solutionavoids the development of stresses within the lens that result in badoptics and lens parameter shifts. Additionally, the binding polymer mustbe swellable in the lens material, permitting swelling of the imageprinted using the colorant of the invention. Due to this swelling, theimage becomes entrapped within the lens material without any impact onlens comfort.

[0023] Pigments useful with the binding polymer in the colorants of theinvention are those organic or inorganic pigments suitable for use incontact lenses, or combinations of such pigments. The opacity may becontrolled by varying the concentration of the pigment and opacifyingagent used, with higher amounts yielding greater opacity. Illustrativeorganic pigments include, without limitation, pthalocyanine blue,pthalocyanine green, carbazole violet, vat orange # 1, and the like andcombinations thereof Examples of useful inorganic pigments include,without limitation, iron oxide black, iron oxide brown, iron oxideyellow, iron oxide red, titanium dioxide, and the like, and combinationsthereof In addition to these pigments, soluble and non-soluble dyes maybe used including, without limitation, dichlorotriazine and vinylsulfone-based dyes. Useful dyes and pigments are commercially available.

[0024] Coating, or wetting, of the pigment particles with bindingpolymer provides better dispersion of the pigment particles in the bulkbinding polymer. The coating may be achieved by use of electrostatic,dispersive, or hydrogen bonding forces to cover the pigment's surface.Preferably, a high shear force is used to disperse the pigment into thebinding polymer. The pigment may be added to the binding polymer bydispensing the polymer and pigment into a suitable mixer, such as arotary shaft mixer and mixing until a homogeneous mixture results,typically for a period of up to about 30 minutes. The mixture may bethen fed into a high shear mill, such as an Eiger mill to disperse thepigment into the binding polymer. Repeated milling is carried out asnecessary to achieve complete dispersion. Generally, milling is carriedout until the pigments are about 0.2 to about 3 microns in size. Millingmay be carried out using any suitable, commercially available deviceincluding, without limitation, a high shear or ball milling device.

[0025] In addition to the pigment and binding polymer, the colorant ofthe invention contains one or more solvents that aid in coating of thecolorant onto a surface. It is another discovery of the invention that,to ensure a colorant that does not bleed or run on the surface to whichit is applied, it is desirable, and preferred, that the colorant have asurface tension below about 27 mN/m. This surface tension may beachieved by treatment of the surface, for example a mold surface, towhich the colorant will be applied. Surface treatments may be effectedby methods known in the art, such as, but not limited to plasma andcorona treatments. Alternatively, and preferably, the desired surfacetension may be achieved by the choice of solvents used in the colorant.

[0026] Thus, the solvents useful in the colorant of the invention arethose solvents that are capable of increasing or decreasing theviscosity of the colorant and aiding in controlling the surface tension.Suitable solvents include, without limitation, cyclopentanones,4-methyl-2-pentanone, 1-methoxy-2-propanol, 1-ethoxy-2-propanol,isopropyl lactate and the like and combinations thereof. Preferably,1-ethoxy-2-propanol and isopropyl lactate are used.

[0027] In a preferred embodiment, at least three different solvents areused in the colorant of the invention. The first two of these solvents,both medium boiling point solvents, are used in the production of thebinding polymer. Although these solvents may be stripped from thebinding polymer after its formation, it is preferred that they areretained. Preferably, the two solvents are 1-ethoxy-2-propanol andisopropyl lactate. An additional low boiling solvent, meaning a solventthe boiling point of which is between about 75 and about 120° C., isused to decrease the viscosity of the colorant as desired. Suitable lowboiling solvents include, without limitation, 2-propanol,1-methoxy-2-propanol, 1-propanol, and the like and combinations thereof.Preferably, 1-propanol is used.

[0028] The specific amount of solvents used will depend on a number offactors. For example, the amount of solvents used in forming the bindingpolymer will depend upon the molecular weight of the binding polymerdesired and the constituents, such as the monomers and copolymers, usedin the binding polymer. The amount of low boiling solvent used willdepend upon the viscosity and surface tension desired for the colorant.Further, if the colorant is to be applied to a mold and cured with alens material, the amount of solvent used will depend upon the lens andmold materials used and whether the mold material has undergone anysurface treatment to increase its wettability. Determination of theprecise amount of solvent to be used is within the skill of oneordinarily skilled in the art. Generally, the total weight of thesolvents used will be about 40 to about 75 weight percent of solventwill be used.

[0029] One ordinarily skilled in the art will recognize that eachpigment used will have a critical pigment volume for the solventsselected. The critical pigment volume may be determined by any knownmeans and, generally, is a volume based on the efficiency of a solventand the binding polymer to suspend the pigment particles for example, asdisclosed in Patton, Temple C., Paint Flow and Pigment Dispersion, 2ded., pp 126-300 (1993).

[0030] In addition to the solvents, a plasticizer may be and, preferablyis, added to the colorant to reduce cracking during the drying of thecolorant and optical mold parts, to enhance the final quality of theimage produced using the colorant, and to enhance the diffusion andswelling of the colorant by the lens material. The type and amount ofplasticizer used will depend on the molecular weight of the bindingpolymer used and, for colorants placed onto molds that are stored priorto use, the shelf-life stability desired. Useful plasticizers include,without limitation, glycerol, propylene glycol dipropylene glycol,tripropylene glycol polyethylene glycol 200, 400, or 600, and the likeand combinations thereof. Preferably, glycerol is used. Amounts ofplasticizer used generally will be 0 to about 10 weight percent based onthe weight of the colorant.

[0031] The opacity of the colorant may be controlled by varying thepigment concentration and the pigment particle size used. Alternatively,an opacifying agent may be used. Suitable opacifying agents, such as forexample titanium dioxide or zinc oxide, are commercially available.

[0032] In a preferred colorant mixture of the invention, about 0.2 toabout 25 weight percent of pigment, about 30 to about 45 weight percentof binding polymer, about 40 to about 70 weight percent of solvents,about 0 to about 25 weight percent of titanium dioxide, and about 0.2 toabout 7 weight percent of plasticizer is used. The weight percentagesare based on the total weight of the colorant mixture.

[0033] The binding polymer may be loaded with about 0.2 to about 25weight percent based on the weight of the colorant for organic pigmentsand about 0.2 to about 50 weight percent for inorganic pigments.However, high pigment concentrations may impart a very dark hue.Therefore, preferably about 0.2 to about 7 weight percent of organicpigments and about 0 to about 20 weight percent of inorganic pigmentsare used. Combinations of pigments may be used in ratios dependent uponthe color, shade, and hue desired.

[0034] One ordinarily skilled in the art will recognize that additivesother than those discussed also may be included in the colorantcomposition of the invention. Suitable additives include, withoutlimitation, additives that aid flow and leveling, additives for foamprevention, additives for rheology modification, and the like, andcombinations thereof.

[0035] The colorant of the invention becomes embedded in the lensmaterial upon curing of the material. Thus, the colorant may embedcloser to the front or back surface of the lens formed depending on thesurface of the mold to which the lens the colorant is applied.Additionally, one or more layers of colorant may be applied in anyorder. In yet another embodiment, a clear binding polymer layer may beused in conjunction with the colorant. For example, in the method of theinvention a clear binding polymer layer may be applied to the moldingsurface of a mold half prior to application of the colorant. The clearbinding polymer may be the same or different from the binding polymerused for the colorant layers. If the clear binding polymer is differentfrom the binding polymer, it must be compatible with the binding polymerand lens material in terms of expansion factor and swellability and itmust be capable of swelling into the lens material.

[0036] The invention may be used to provide tinted hard or soft contactlenses made of any known lens material, or material suitable formanufacturing such lenses. Preferably, the lenses of the invention aresoft contact lenses having water contents of about 0 to about 90percent. More preferably, the lenses are made of monomers containinghydroxy groups, carboxyl groups, or both or be made fromsilicone-containing polymers, such as siloxanes, hydrogels, siliconehydrogels, and combinations thereof. Material useful for forming thelenses of the invention may be made by reacting blends of macromers,monomers, and combinations thereof along with additives such aspolymerization initiators. Suitable materials include, withoutlimitation, silicone hydrogels made from silicone macromers andhydrophilic monomers. Examples of such silicone macromers include,without limitation, polydimethylsiloxane methacrylated with pendanthydrophilic groups as described in U.S. Pat. Nos. 4,259,467; 4,260,725and 4,261,875; polydimethylsiloxane macromers with polymerizablefunction described in U.S. Pat. Nos. 4,136,250; 4,153,641; 4,189,546;4,182,822; 4,343,927; 4,254,248; 4,355,147; 4,276,402; 4,327,203;4,341,889; 4,486,577; 4,605,712; 4,543,398; 4,661,575; 4,703,097;4,837,289; 4,954,586; 4,954,587; 5,346,946; 5,358,995; 5,387,632;5,451,617; 5,486,579; 5,962,548; 5,981,615; 5,981,675; and 6,039,913;and combinations thereof. They may also be made using polysiloxanemacromers incorporating hydrophilic monomers such as those described inU.S. Pat. Nos. 5,010,141; 5,057,578; 5,314,960; 5,371,147 and 5,336,797;or macromers comprising polydimethylsiloxane blocks and polyether blockssuch as those described in U.S. Pat. Nos. 4,871,785 and 5,034,461. Allof the cited patents are hereby incorporated in their entireties byreference.

[0037] Suitable materials also may be made from combinations of oxypermand ionoperm components such as is described in U.S. Pat. Nos.5,760,100; 5,776,999; 5,789,461; 5,807,944; 5,965,631 and 5,958,440.Hydrophilic monomers may be incorporated into such copolymers, including2-hydroxyethyl methacrylate (“HEMA”), 2-hydroxyethyl acrylate,N,N-dimethylacrylamide (“DMA”), N-vinylpyrrolidone,2-vinyl-4,4-dimethyl-2-oxazohn-5-one, methacrylic acid, and2-hydroxyethyl methacrylamide. Additional siloxane monomers may beincorporated such as tris(trimethylsiloxy)silylpropyl methacrylate, orthe siloxane monomers described in U.S. Pat. Nos. 5,998,498; 3,808,178;4,139,513; 5,070,215; 5,710,302; 5,714,557 and 5,908,906. They may alsoinclude various toughening agents, UV blockers, and wetting agents. Theycan be made using diluents such as primary alcohols, or the secondary ortertiary alcohols described in U.S. Pat. No. 6,020,445. All of the citedpatents are hereby incorporated in their entireties by reference.

[0038] The materials for making the contact lenses are well known andcommercially available. Preferably, the material used is a HEMA basedhydrogel, more preferably etafilcon A, and the binding polymer is formedfrom linear random block copolymers of MAA, HEMA and lauryl methacrylate(“LMA”); linear random block copolymers of MAA and HEMA; linear randomblock copolymers of HEMA and LMA; or a HEMA homopolymer. Etafilcon A,disclosed in U.S. Pat. Nos. 4,680,336 and 4,495,313 incorporated hereinin their entireties by reference, generally is a formulation of 100parts by weight (“pbw”) HEMA, about 1.5 to about 2.5 pbw MAA,approximately 0.3 to about 1.3 pbw ethylene glycol dimethacrylate, about0.05 to about 1.5 pbw 1,1,1,-trimethylolpropane trimethacrylate, andabout 0.017 to about 0.024 pbw of a visibility tint. Preferablyetafilcon A is used with a linear random block copolymer of MAA, HEMAand LMA in a ratio of 0.47 MAA to 100 HEMA to 4.14 LMA, or with a linearrandom block copolymer of HEMA and MAA in a ratio of 99.9 HEMA and 0.1MAA to 99.5 HEMA and 0.5 MAA.

[0039] A tinting-effective amount of the colorant is used which is anamount sufficient to impart the desired level of tint to the lens to beproduced. Generally, about 0.5 mg to about 4.0 mg of colorant is usedper lens.

[0040] The colorant used in the lenses of the invention are applied tothe lens surface by any convenient method. In a preferred method of theinvention, a thermoplastic optical mold, made from any suitable materialincluding, without limitation, polypropylene or polystyrene resin isused. A tinting-effective amount of the colorant is applied to thedesired portion of the molding surface of the mold. Application may becarried out by any convenient means. Preferably, application is carriedout by pad printing.

[0041] A lens-forming amount of a lens material is dispensed into themold. By “lens-forming amount” is meant an amount sufficient to producea lens of the size and thickness desired. Typically, about 10 to about40 mg of lens material is used.

[0042] The colorant is swelled in the lens material. Preferably, theswelling is carried out under conditions suitable to swell the colorantto about 1 to about 4 times its dried thickness. Typically, suchswelling may be achieved in from about 1 to about 30 minutes at about 40to about 68° C.

[0043] The mold containing the lens material and colorant then isexposed to conditions suitable to form the tinted lens. The preciseconditions will depend upon the components of the colorant and lensmaterial selected and are within the skill of one of ordinary skill inthe art to determine. Once curing is completed, the lens is releasedfrom the mold and may be equilibrated in a buffered saline solution.

[0044] A preferred method of manufacturing a tinted lens is carried outusing pad printing as follows. A metal plate, preferably made from steeland more preferably from stainless steel, is covered with a photo resistmaterial that is capable of becoming water insoluble once cured. Thepattern for the colorant is selected or designed and then reduced to thedesired size using any of a number of techniques such as photographictechniques, placed over the metal plate, and the photo resist materialis cured. Conditions for carrying out the pattern etching are within theknowledge of one ordinarily skilled in the art.

[0045] Following the pattern, the plate is subsequently washed with anaqueous solution and the resulting image is etched into the plate to asuitable depth, for example about 20 microns. The colorant is thendeposited onto the pattern to fill the depressions with colorant. Asilicon pad of a suitable geometry and varying hardness, generally about1 to about 10 Shore A durometer units, is pressed against the image onthe plate to remove the colorant and the colorant is then dried slightlyby evaporation of the solvent. The pad is then pressed against themolding surface of an optical mold and the colorant s allowed to dry.The mold is degassed for up to 12 hours to remove excess solvents andoxygen after which the mold is filled with lens forming amount of a lensmaterial. A complementary mold half is then used to complete the moldassembly and, after the printed image is allowed to swell, the moldassembly is exposed to conditions suitable to cure the lens materialused.

[0046] The invention will be clarified further by consideration of thefollowing, non-limiting examples.

EXAMPLES Example 1 Synthesis of Binding Polymer

[0047] To a 5 L glass container was added 2.65 wt percent ofdodecanethiol, 1.56 wt percent lauryl methacrylate, 0.18 wt percent MAA,37.69 wt percent 2-HEMA, and 42.35 wt percent isopropyl lactate and10.59 wt percent 1-ethoxy-2-propanol as solvents. The mixture waspremixed for 10 min. using a magnetic stirrer and then transferred to a5 L stainless steel reactor with a built-in heating mantel and equippedwith a mechanical stirrer, nitrogen inlet, reflux condenser, and atemperature sensor. The mixture was heated to a temperature ofapproximately 630 C for approximately 25 min, at which point 3.0 wtpercent of 2,2-azobis-2-methyl butyronitrile were added with residualisopropyl lactate. Nitrogen was introduced into the reactor to create anitrogen blanket to be used during the remainder of the polymerization.

[0048] After approximately 17 to 19 hrs, 1.96 wt percent of glycerolwere added to the reaction mixture and the mixture was stirred forapproximately 30 min. Subsequently, the stirring and nitrogen supplywere discontinued and the reaction mixture cooled to room temperature.

Example 2 Synthesis of Binding Polymer

[0049] To a 5 L glass container was added 0.69 wt percent ofdecanethiol, 0.16 wt percent MAA, 33.55 wt percent 2-HEMA, and 51.1 wtpercent isopropyl lactate and 12.8 wt percent 1-ethoxy-2-propanol assolvents. The mixture was premixed for 10 min. using a magnetic stirrerand then transferred to a 5 L stainless steel reactor with a built-inheating mantel and equipped with a mechanical stirrer, nitrogen inlet,reflux condenser, and a temperature sensor. The mixture was heated to atemperature of approximately 68° C. for approximately 25 min, at whichpoint 0.20 wt percent of 2,2-azobis-2-methyl butyronitrile were addedwith residual isopropyl lactate. Nitrogen was introduced into thereactor to create a nitrogen blanket to be used during the remainder ofthe polymerization.

[0050] After approximately 17 to 19 hrs, 1.56 wt percent of glycerolwere added to the reaction mixture and the mixture was stirred forapproximately 30 min. The reaction mixture was heated at 80° C. for anadditional 23 hours in order to decompose the residual thermalinitiator. Subsequently, the stirring and nitrogen supply werediscontinued and the reaction mixture cooled to room temperature.

Example 3

[0051] Binding polymers similar to or the same as those of Example 1were used to make the colorant formulations listed on the table below.Color- Color- Color- Color- Color- ant 1 ant 2 ant 3 ant 4 ant 5Colorant 6 Pthalo- 2 0 0 2 0 0 cyanine Blue Iron Oxide 0 10 0 3 5 0Black Iron Oxide 0 0 3 15 5 0 Yellow Iron Oxide 0 0 8 0 5 0 Brown IronOxide 0 0 2 0 0 0 Red TiO₂ 0 5 5 5 5 0 Total 0 15 18 25 20 0 PigmentsBinding 41.49 35.63 34.28 31.12 33.37 42.39 Polymer Isopropyl- 38.9633.46 32.19 29.22 31.34 39.81 lactate 1-ethoxy-2- 9.74 8.37 8.05 7.317.84 9.95 propanol 1-propanol 6 6 6 6 6 6 Glycerol 1.96 1.96 1.96 1.961.96 1.96

Example 4

[0052] To the binding polymer of Example 1 was added 0.5 wt % ofphthalo-cyanine blue pigment and milled to form a blue colorant. Analiquot of the colorant was then pad printed onto a contact lens frontcurve mold and the printed mold was degassed under vacuum, about 8hours, in order to remove the volatile solvents from the colorant. Theprinted mold was dosed with a reactive monomer mixture containing 1100parts by weight (“pbw”) HEMA, about 2 pbw MAA, approximately 0.8 pbwethylene glycol dimethacrylate, about 0.1 pbw 1,1,1,-trimethylolpropanetrimethacrylate, about 1 pbw Norbloc® 7966 and about 1.3 pbw Irgacure(photoinitiator, commercially available from Ciba). A contact lens basecurve mold was deposited onto the filled front curve mold and the twomold halves were pressed together. A dwell time of approximately twominutes allowed the reactive monomer mix to diffuse into and around thecolorant layer, resulting in the swelling of the colorant layer. Aftercompletion of the dwell time, the mold assembly was exposed to visiblelight (approximately 420 nm) for approximately five minutes, whereuponthe reactive monomer mixture was polymerized and cross-linked in andaround the binding polymer of the colorant layer, forming thesemi-interpenetrating polymer network. The mold halves were separatedand the tinted lens removed for further processing steps. Thus, thepresent example shows that a tinted contact lens may be formed from abinding polymer, which is not substantially cross-linked and a base lensmaterial which is cross-linked after diffusing into and around thebinding polymer. Beneficially, the pigments which were mixed into thebinding polymer are fixed in the resultant contact lens without the needfor functionalization or additional bonding steps.

What is claimed is:
 1. A colorant for use in tinting contact lenses, thecolorant comprising one or more pigments, one or more solvents, and abinding polymer, wherein the binding polymer is capable of forming aninterpenetrating polymer network with a lens material.
 2. The colorantof claim 1, wherein the interpenetrating polymer network formed is asemi-interpenetrating polymer network.
 3. The colorant of claim 1,wherein the interpenetrating polymer network formed is asequential-interpenetrating polymer network.
 4. The colorant of claim 1,wherein the binding polymer comprises a molecular weight of about 7,000to about 40,000.
 5. The colorant of claim 1, wherein the binding polymercomprises: CH₃(CH₂)_(x)—L—COCHR═CH₂ wherein L is —NH or oxygen, x is awhole number from 2 to 24, R is a C₁ to C₆ alkyl or hydrogen.
 6. Thecolorant of claim 1, wherein the binding polymer comprises a copolymerof methacrylic acid, 2-hydroxyethyl methacrylate, and laurylmethacrylate.
 7. The colorant of claim 1, wherein the binding polymercomprises a copolymer of 2-hydroxyethyl methacrylate and methacrylicacid.
 8. The colorant of claim 1, wherein the binding polymer comprisesa homopolymer of 2-hydroxyethyl methacrylate.
 9. The colorant of claim1, 2, 3, 4, 6, 7 or 8, wherein the one or more solvents comprises atleast one medium boiling point solvents and one low boiling pointsolvent.
 10. The colorant of claim 1, 2, 3, 4, 6, 7 or 8, wherein thesurface tension is ≦28 dynes/cm.
 11. The colorant of claim 6,7 or 8wherein the medium boiling point solvents comprise l-ethoxy-2-propanoland isopropyl lactate.
 12. The colorant of claim 1, 2, 3, 4, 6, 7 or 8,further comprising a plasticizer and an opacifying agent.
 13. Thecolorant of claim 12, comprising about 0.2 to about 25 weight percent ofthe one or more pigments, about 30 to about 45 weight percent of thebinding polymer, about 40 to about 70 weight percent of the one or moresolvents, about 0 to about 25 weight percent of the opacifying agent,and about 0.2 to about 7 weight percent of the plasticizer.
 14. Acolorant for use in tinting contact lenses, the colorant comprising oneor more pigments, one or more solvents, and a binding polymer having amolecular weight of about 7,000 to about 40,000, wherein the bindingpolymer is capable of forming a interpenetrating polymer network with alens material comprising a HEMA-based hydrogel or a silicone-basedhydrogel.
 15. The colorant of claim 14, wherein the interpenetratingpolymer network formed between the binding polymer and the lens materialis a semi-interpenetrating polymer network
 16. The colorant of claim 14,wherein the interpenetrating polymer network formed between the bindingpolymer and the lens material is a sequential interpenetrating polymernetwork
 17. The colorant of claim 14, wherein the binding polymercomprises a copolymer of methacrylic acid, 2-hydroxyethyl methacrylate,and lauryl methacrylate.
 18. The colorant of claim 14, wherein thebinding polymer comprises a copolymer of methacrylic acid and2-hydroxyethyl methacrylate.
 19. The colorant of clam 14, wherein thebinding polymer comprises a homopolymer of 2-hydroxyethyl methacrylate.20. The colorant of claims 14-19, wherein the one or more solventscomprises two medium boiling point solvents and one low boiling pointsolvent.
 21. The colorant of claim 20, wherein the two medium boilingpoint solvents comprise 1-ethoxy-2-propanol and isopropyl lactate. 22.The colorant of claims 14-19 further comprising a plasticizer and anopacifying agent.
 23. The colorant of claim 22, comprising about 0.2 toabout 25 weight percent of the one or more pigments, about 30 to about45 weight percent of the binding polymer, about 40 to about 70 weightpercent of the one or more solvents, about 0 to about 25 weight percentof the opacifying agent, and about 0.2 to about 7 weight percent of theplasticizer.
 24. A method for manufacturing a tinted contact lenscomprising the steps of: a.) applying to a molding surface of a mold atinting-effective amount of a colorant comprising one or more pigments,one or more solvents and a binding polymer; b.) dispensing alens-forming amount of a lens material into the mold; c.) swelling thecolorant in the lens material; and d.) curing the lens material in themold to form the tinted contact lens, wherein the binding polymer andthe lens material form an interpenetrating polymer network.
 25. Themethod of claim 24, wherein the binding polymer has a molecular weightof about 7,000 to about 40,000 and the lens material comprises HEMAbased hydrogels or silicone-based hydrogels.
 26. The method of claim 24,wherein the binding polymer comprises a copolymer of methacrylic acid,2-hydroxyethyl methacrylate, and lauryl methacrylate.
 27. The method ofclaim 24, wherein the binding polymer comprises a copolymer ofmethacrylic acid and 2-hydroxyethyl methacrylate.
 28. The method ofclaim 24, wherein the binding polymer comprises a homopolymer of2-hydroxyethyl methacrylate.
 29. The method of claim 24 or 25, whereinthe one or more solvents comprises two medium boiling point solvents andone low boiling point solvent.
 30. The method of claim 29, wherein thetwo medium boiling point solvents comprise 1-ethoxy-2-propanol andisopropyl lactate.
 31. A mold for use in manufacturing a tinted contactlens comprising a first and second mold half, wherein at least onemolding surface of the first and second mold halves comprises one ormore pigments, one or more solvents, and a binding polymer, wherein thebinding polymer is capable of forming an interpenetrating polymernetwork with a lens material.
 32. The mold of claim 31, wherein theinterpenetrating polymer network formed between the binding polymer andthe lens material is a semi-interpenetrating polymer network.
 33. Themold of claim 31, wherein the interpenetrating polymer network formedbetween the binding polymer and the lens material is a sequentialinterpenetrating polymer network.
 34. The mold of claim 31, wherein thebinding polymer has a molecular weight of about 7,000 to about 40,000.35. The mold of claim 31, wherein the binding polymer comprises acopolymer of methacrylic acid, 2-hydroxyethyl methacrylate, and laurylmethacrylate.
 36. The mold of claim 31, wherein the binding polymercomprises a copolymer of methacrylic acid and 2-hydroxyethylmethacrylate.
 37. The mold of claim 31, wherein the binding polymercomprises a homopolymer of 2-hydroxyethyl methacrylate.
 38. The mold ofclaims 31-37 wherein the one or more solvents comprises two mediumboiling point solvents and one low boiling point solvent.
 39. The moldof claim 38, wherein the two medium boiling point solvents comprise1-ethoxy-2-propanol and isopropyl lactate.
 40. The ophthalmic lensderived from the colorant of claim 23, the method of claim 30 and themold of claim
 39. 41. The method of claim 24 wherein said pigment iscoated or wetted with said binding polymer.